This policy is not for everyone!
If you are working in pure ASCII,
then disable it now or you may see some false violations.

On the other hand many of us are working in a multilingual world with an extended character set,
probably Unicode.
In that world,
patterns like m/[A-Z]/ can be a source of bugs when you really meant m/\p{IsUpper}/.
This policy catches a selection of possible incorrect character class usage.